Four F-16s and one Romanian MiG-21 LanceR took off from Romania’s Campia Tarzii military base as the Dacian Viper 2014 exercises began. The weeklong exercise at the base 300 kilometers (190 miles) northwest of Bucharest — the fourth of its kind between the two nations— was planned before Russia’s annexation of Crimea last month.

Wing Commander Marian Petrus, commander of 71 Air Base, said Romanian pilots will be trained to fly F-16s.

“The purpose of the exercise is to train in techniques and practices used by NATO armies. The final objective is to raise the level of training for the young pilots,” said Wing Commander Adrian Motorga of the 711 Fighter Squadron.

NATO’s eastern nations have been calling on the alliance to beef up its presence following the annexation and related tensions involving Ukraine. Romania, Ukraine and Russia all border the Black Sea.

NATO has already reinforced its Baltic air patrols and is performing daily AWACs surveillance flights over Poland and Romania. The U.S. said this month it was sending new troops and aircraft to a Romanian base near the Black Sea, a decision made before Russia took control of Crimea.

Romania’s defense ministry signed a deal in October to buy secondhand F-16 fighter jets from Portugal to bring its air force up to NATO standards.